150 J. SMITH ON THE GENERA OF FERNS. 



Davallia, or Cheilanthes, they are produced on lengthened 

 rachis-Hke parts of the rhizoma, which are smooth or acule- 

 ate ; it is difficult to say under what circumstances or modi- 

 fications of structure this singular growth is produced, but 

 probably I am not far wrong in stating that it may be con- 

 sidered as analogous to the Trichomanoid growth, found on 

 the stipes of Hemitelia capensis. 



40. PoLYBOTRYA, Humb. Kaulf. 



(Acrostichi, Sp. Sw. Hook. Khipidopteris, Schott. Ege- 



nolfia, Schott.) 



Feins radiating and forked, or costseform and pinnate, ex- 

 ternal; venules simple, free; sporangia occupying one or both 

 sides of the spiciform segments. 



Fronds pinnate, bi- or tripinnatet rarely digitate and lacinia- 

 ted. Sterile pinnules crenate or pinnatijid. Fertile linear or 

 racemose, bearing the sporangia on one, or generally on both 

 sides, or in distinct irregular masses. 



* Rhipidopteris, Schott. 



Fronds flabellate, digitate-multipartite, or entire. 

 Examp. I. P. peltata, {Sw.) 2. P. tripartita, {Hook.) 3. 

 P. foeniculaceum, {Hook.) 4. P. bifurcata, {Sw.) 



** PoLYBOTRYA VERA. 



Fronds pinnate, or bi-tripinnate. 



5. P. vivipara, {Hook.) 6. P. appendiculata, {fVilld.) 7. 

 P. cylindrica, Kaulf. 8. P. speciosa, Schott. 9. P. acu- 

 minata, Kaulf. 10. P. incisa. Link. 11. P. osmundacea, 

 Humb. Illust. Schott. Gen. Fil. t. 7, 16. Hook. Gen. FH- 

 t. 78. b. 



Obs, Although this genus is distinct in habit from the two 

 preceding genera, yet it is very difficult to characterize them as 

 distinct by their venation : this is especially the case with those 

 species of Polybotrya, which have their fertile segments not 

 so much contracted as in others, and bearing the sporangia 

 only on the under side; the most obvious difference is in the 



